Prosthetic devices which are implanted for replacement of joints are well known. Such implants take the place of native joints. Implants may be used for patients suffering from rheumatism and degenerative or traumatic arthritis, including osteoarthritis. The ankle joint, or the joint between the tibia, fibula and the talus, is frequently a source of osteo or rheumatoid arthritis. Formerly, sufferers of rheumatoid or osteoarthritis at the ankle joint have been generally limited to a procedure called fusing. In a fusing procedure, the tibia, and typically the fibula, are fused or secured together with the talus to reduce the patient's pain and improve mobility. Of course, fusing a joint does not provide the same degree of motion as a joint which is not fused.
The design of a replacement joint, however, is complicated by various considerations. For example, the replacement joint should not occupy more space in the body than the natural joint. Additionally, the replacement joint must be connected with the bone and tissue remaining after surgery. Moreover, obtaining surgical access to the joint typically destroys some tissue which provides support for the native joint. Thus, a replacement joint must not only have sufficient strength and durability to withstand the weight and stresses which are applied to a native joint, the replacement joint must further be configured to withstand additional stresses not typically applied to a native component.
Ankle joints pose additional problems due to the shifting of weight and type of motion required for walking. Thus, matching the pivot point of the joint is critical, as misalignment can lead to difficulty in walking and other motions, which may cause the patient considerable pain.
The durability of a replacement joint is also important. The high stresses experienced by an ankle replacement during walking, running, and jumping, all of which are compounded over time, may crack or fracture ankle components of replacement joints, which absorb a substantial amount of the pressures during the aforementioned activities.
A particularly successful ankle implant for use in total ankle arthroscopy is disclosed in U.S. Pat. No. 5,326,365 to Alvine. The total ankle implant, as disclosed in U.S. Pat. No. 5,326,365, is marketed by DePuy Orthopaedics, Inc. under the name Agility™ Ankle. This type of ankle prosthesis performs quite well on patients having a primary or initial total ankle arthroplasty. Occasionally, however, the talus of the patient may be in such a condition that the talus does not provide sufficient support for the total ankle prosthesis.
When there is insufficient support for an ankle prosthesis, or as osteoarthritis or rheumatoid arthritis or aging progresses, a prosthesis may subside into the talus and may eventually pass through the talus into calcaneus. Additionally, the forgoing processes may results in aseptic loosening of the ankle prosthesis.
Loosened or subsided components may result in bone loss and cause severe pain to the patient. Additionally, subsidence of the ankle prosthesis may result in reduced motion of the ankle. For example, the loosening and the subsidence of an ankle prosthesis may result in loss of plantar flexion. Further subsidence and loosening of the ankle prosthesis may also limit the inversion and eversion movements of the ankle.
The loosening and subsidence of an ankle prosthesis usually occurs with massive bone loss to the talus and as stated earlier, the prosthesis may subside down into the calcaneus. The mere replacement of the original prosthesis with another larger component is generally is not successful in correcting the problem.
Attempts to address the revision of the total ankle arthroplasty have met with limited success. Once the primary ankle prosthesis has loosened and subsided, the typical surgical procedure is to fuse the ankle. In such a procedure a metal rod is inserted through the calcaneus through the talus into the tibia to fuse or lock the talus to the tibia.
With some very limited success, some failed primary total ankle arthroplasty prostheses have been replaced with a revision total ankle arthroplasty. The prosthesis for such procedures may need to be specially designed and specially built. These prostheses can be very specific expensive and provide the surgeon with only one very specific implant option in time of the surgery. Additionally, the implantation of such custom devices is often a very technically demanding procedure as instrumentation and surgical procedures are not well established.
Therefore, a need exists for an ankle prosthesis that provides improved support for a wide range of patient anatomies and disease states. A further need exists for an ankle prosthesis which is easily replaced when the articulating portion of the prosthesis becomes worn.